1. Field of the Invention
This invention relates in general to data storage systems, and more particularly to a slider air bearing design and method providing writing of laser field measurement without substantial fly height affect.
2. Description of Related Art
Fixed magnetic disk systems, typically referred to as xe2x80x9chardxe2x80x9d disk drives, are now commonplace as the main non-volatile storage in modern personal computers, workstations, and portable computers. Such hard disk drives are now capable of storing gigabyte quantities of digital data, even when implemented in portable computers of the so-called xe2x80x9cnotebookxe2x80x9d class. Many important advances have been made in recent years that have enabled higher data density and thus larger storage capacities of hard disk drives, and that have also enabled much faster access speeds, both in the bandwidth of data communicated to and from the hard disk drive, and also in the access time of specified disk sectors. Advances have also been made that have greatly reduced the size and weight of hard disk drives, particularly as applied to portable computers, have been made over recent years. These advances have resulted in the widespread availability of ultra-light portable computers, yet having state-of-the art capability and performance.
A head/disk assembly typically comprises one or more commonly driven magnetic disks rotatable about a common spindle and cooperating with at least one head actuator for moving a plurality of transducers radially relative to the disks so as to provide for the reading and/or writing of data on selected circular tracks provided on the disks. The magnetic transducer or xe2x80x9cheadxe2x80x9d is suspended in close proximity to a recording medium, e.g., a magnetic disk having a plurality of concentric tracks. The transducer is supported by an air bearing slider mounted to a flexible suspension. The suspension, in turn, is attached to a positioning actuator.
During normal operation, relative motion is provided between the head and the recording medium as the actuator dynamically positions the head over a desired track. The relative movement provides an air flow along the surface of the slider facing the medium, creating a lifting force. The lifting force us counterbalanced by a predetermined suspension load so that the slider is supported on a cushion of air. Air flow enters the leading edge of the slider and exits from the trailing end. The head resides near the trailing end, which tends to fly closer to the recording surface than the leading edge.
The recording medium holds information encoded in the form of magnetic transitions. The information capacity, or areal density, of the medium is determined by the transducer""s ability to sense and write distinguishable transitions. An important factor affecting areal density is the distance between the transducer and the recording surface, referred to as the fly height. It is desirable to fly the transducer very close to the medium to enhance transition detection. Fly height stability is determined by proper suspension loading and by shaping the air bearing slider surface (ABS) for desirable aerodynamic characteristics.
One important design factor for fly height is the slider""s resistance to changing conditions. If the transducer fly height does not stay constant during changing conditions, data transfer between the transducer and the recording medium may be adversely affected. Fly height is further affected by physical characteristics of the slider such as the shape of the ABS. Optimized rail shaping, for example, can provide enough resistance to changes in air flow.
Hard drive manufactures are starting to incorporate proximity recording type sliders in drives in order to achieve higher storage densities. The proximity recording slider is designed to maintain a small area near the read-write element in constant contact with the disk, and thus enabling smaller bit size and ultimately larger storage densities. This approach to increasing storage density puts considerable amount of strain on controlling wear at the slider-disk interface, because a slight variation in contact load and contact area could greatly affect the drive survivability.
Slider-disk contact results in lubricant depletion and degradation, wear of both surfaces, generation of wear particles, stick-slip, etc. All these phenomena affect reliability of the disk drive, e.g., through jitter, as well as its durability.
To continue the increases being made in data-storage density, drive designs call for lower and lower slider fly height. For a magnetic head slider with an ABS pattern, there are numerous slider-curvature parameters and curvature-adjust techniques (CATs) that are considered important for fly height control and tribology. Crown is the maximum separation of the cylindrical contour along the flying direction from an imaginary plane drawn between the leading and trailing edges of the ABS. Camber has a similar definition and is the separation from an imaginary plane drawn perpendicular to the flying direction between the two side edges of the slider. Twist is the difference of the xe2x80x9cdiagonalxe2x80x9d cylindrical curvatures.
For modern pico sliders, these curvature parameters are typically on the order of several nanometers, while the slider width and length are about 1 mm. The actual curvatures of the ABS are therefore truly minute. However, the variance of the crown is a key factor in slider performance.
Fly-height modeling of common xe2x80x9cnegative-pressure air bearingxe2x80x9d sliders indicates that small changes of a few nanometers in the crown can significantly affect the fly height of the slider. Hence there has been an obvious need to develop and implement a method to finely adjust crown.
One technique involves for adjusting crown is xe2x80x9claser scribingxe2x80x9d, which refers to the exposure of the slider surface-typically the back or flex side-to sufficiently intense laser irradiation such that a permanent surface modification is produced. The technique of laser scribing to produce surface-stress change is very desirable because laser scribing is non-contact and fast, and there is no mechanical wear and tear of any contact device like a grinding wheel or a diamond scriber; it is more precise, since the positioning of the focused laser beam can be accurately controlled using galvo mirrors and machine vision; and it is more amenable to an in-situ closed-loop control that terminates the scribing when the target crown or camber is reached.
Preferably, laser scribing is performed on the flex side to induce positive curvature changes at the ABS. This is a significant advantage compared to scribing or modifying the ABS side, since any debris that is not cleaned or washed away is much less offensive at the flex side compared to the ABS side. The use of a high-pulse-repetition-rate laser permits rapid processing of the slider by quickly scanning the spot on the surface to produce the scribe pattern required to provide the desired curvature change.
There are various non-contact optical techniques for in-situ monitoring of slider curvature that provide closed-loop control with laser scribing. Applicable optical monitoring techniques include probe-beam deflection sensing (PDS) techniques-used frequently in atomic force microscopy and photothermal beam-deflection spectroscopy and interferometer imaging.
However, one approach involves the xe2x80x9cWriting Of a Laser Fieldxe2x80x9d (WOLF) on suitable areas of the slider ABS surface by telecentric scanning of a probe laser beam and monitoring the directions of the scanning reflected laser beam. This WOLF technique is basically a multi-beam differential PDS technique. As a result, it is insensitive to static tilts of the slider surface, unlike the single-beam PDS method. Compared to interferometry, the WOLF method is much faster-providing a crown measurement in 10 milliseconds rather than a few seconds, as in interferometric techniques. Nonetheless, the WOLF method does not typically provide an absolute measurement of crown or camber and so the WOLF measured values have to be converted to a crown value via a calibration procedure that produces a lookup table.
For example, one slider design, Negative Pressure Bobsled Slider (NPBS), is widely used in mobile, desktop, and server products, as well as OEM head products because of its superior flying performances and easiness in ABS design. NPBS has two separated front ABS pads and one island pad at the trailing end. Typically these pads are surrounded by ion milled pads to produce step tapers. In view of the above discussions regarding crown, one common aspect observed for NPBS is that fabrication crown is one of the key process parameters controlling fly height variations. Several method have been used to measure and adjust crown during fabrication to improve process capability without sacrificing the throughput.
The most advanced method up to date is to use the above-described WOLF method as the measurement system for crown adjust. As mentioned, the most important advantage of the WOLF process is its speed which allows every slider to be measured multiple times during crown adjust while still maintaining an acceptable throughput. However, a major problem exists when using the WOLF process to measure the crown of the NPBS type of ABS. The problem is that the crown values given by the WOLF process do not always correlate well with those measured by the optical interferometer even when the WOLF measurement system is calibrated using actual sliders with known interferometric crown values. Because crown measured using interferometers is considered more accurate and is the widely accepted industry standard, without a good correlation, the WOLF process cannot be a totally independent measurement system and its application is greatly limited.
Another problem of the WOLF system is that it requires good reflective areas with minimum size of 150 micrometerxc3x97150 micrometer at both front and rear side of the slider. From ABS design point of view, to have two front pads of larger than 150 micrometerxc3x97150 micrometer in size is not a problem. However, the pad geometry constraints imposed on rear pad degrades fly height performance. The larger rear pad geometry makes the fly height sensitive to the crown.
It can be seen that there is a need for a slider air bearing design that allows correlation of WOLF crown measurement values with crown measurements obtain via optical interferometer.
It can also be seen that there is a need for slider air bearing design that provides good reflective areas while preventing degradation in fly height performance due to the rear pad geometry constraints required by the WOLF measurement process.
To overcome the limitations in the prior art described above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, the present invention discloses a slider air bearing design and method providing writing of laser field measurement without substantial fly height affect.
The present invention solves the above-described problems by providing a central pad at ion-mill height in the cavity between the side rails and rear pad. The central pad allows correlation of WOLF crown measurement values with crown measurements obtain via optical interferometer. Also, the central pad provides good reflective areas while preventing degradation in fly height performance due to the rear pad geometry constraints required by the WOLF measurement process.
A slider in accordance with the principles of the present invention includes a slider body having a surface with a leading edge, a trailing edge and first and second side edges, first and second front air bearings positioned at the leading edge of the slider body along the first and second side edges, the first and second front air bearings including first and second front pads and a height selected for a predetermined fly height and second stepped surface side rails at an ion-milling height, a rear pad extending from the trailing edge and located substantially centrally between said sides of said slider, the rear pad including stepped surfaces at an ion-milling height, a negative pressure cavity positioned in the center of the slider body between the side rails and an ion-milling height center pad for providing a good reflective area for WOLF slider curvature measurements while insubstantially affect fly height, the center pad being positioned at the center of the slider within the negative pressure cavity.
Other embodiments of a slider in accordance with the principles of the invention may include alternative or optional additional aspects. One such aspect of the present invention is that the WOLF slider curvature measurements requires a minimum surface area, and wherein the center pad in combination with the rear pad meet the minimum surface area requirement with the center pad removing a size constraint on the rear pad.
Another aspect of the present invention is that the center pad enables the rear pad to be optimized to improve slider performance.
Another aspect of the present invention is that the slider curvature measurements comprise slider crown measurements and the slider performance comprises crown sensitivity.
Another aspect of the present invention is that the center pad comprises angled edges to help smooth particle trajectory, and maximize the effective surface area along the path of the WOLF slider curvature measurements.
Another aspect of the present invention is that the center pad allows an angle for the rear pad to be measured independently from the angle for the first and second front pads.
Another aspect of the present invention is that the center pad decouples the slider curvature measurements of the front pads and the rear pad and enables the use of a combined top pad and rear pad angle to model fly height rather than the traditionally defined crown.
Another aspect of the present invention is that the center pad is formed at a height between 180 nanometers and 280 nanometers below the height of the first and second front pads and the rear pad.
Another aspect of the present invention is that the ion-mill height of the center pad is at least 6 times higher than the fly height measured at the pole tip.
Another aspect of the present invention is that the center pad has a width of 150 micrometers along the path of slider curvature measurements.
In another embodiment of the present invention a disk drive is provided. The disk drive includes at least one rotating disk, a recording medium, disposed on the at least one rotating disk, the recording medium dragging air as the disk rotates and creating an air flow in parallel with a tangential velocity of the disk rotation, an actuator assembly disposed adjacent the at least one rotating disk for positioning a suspension assembly relative to the recording medium and a slider disposed at a distal end of the suspension assembly for supporting a transducer above the rotating disk, the slider further comprising a slider body having a surface with a leading edge, a trailing edge and first and second side edges, first and second front air bearings positioned at the leading edge of the slider body along the first and second side edges, the first and second front air bearings including first and second front pads and a height selected for a predetermined fly height and second stepped surface side rails at an ion-milling height, a rear pad extending from the trailing edge and located substantially centrally between said sides of said slider, the rear pad including stepped surfaces at an ion-milling height, a negative pressure cavity positioned in the center of the slider body between the side rails and an ion-milling height center pad for providing a good reflective area for WOLF slider curvature measurements while insubstantially affect fly height, the center pad being positioned at the center of the slider within the negative pressure cavity.
In another embodiment of the present invention a method for making a slider with a central pad for facilitating WOLF slider curvature measurements is provided. The method includes forming a slider body having a surface with a leading edge, a trailing edge and first and second side edges, forming first and second front air bearings at the leading edge of the slider body along the first and second side edges, the first and second front air bearings including first and second front pads and a height selected for a predetermined fly height and second stepped surface side rails at an ion-milling height, forming a rear pad extending from the trailing edge and located substantially centrally between said sides of said slider, the rear pad including stepped surfaces at an ion-milling height, forming a negative pressure cavity in the center of the slider body between the side rails and forming an ion-milling height center pad for providing a good reflective area for WOLF slider curvature measurements while insubstantially affect fly height, the center pad being positioned at the center of the slider within the negative pressure cavity.
These and various other advantages and features of novelty which characterize the invention are pointed out with particularity in the claims annexed hereto and form a part hereof. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to accompanying descriptive matter, in which there are illustrated and described specific examples of an apparatus in accordance with the invention.